Field of the Invention
The current invention relates to phenolic spheres having improved viscoelasticity and decomposition temperature and a method of their making.
Description of the Art
Phenolic spheres are produced by combining phenol with formalin (an aqueous solution of formaldehyde) in the presence of a catalyst and an emulsion stabilizer. When processed under appropriate conditions spheres of a phenolic resin are formed. Inherently cured phenolic spheres thus formed are traditionally brittle and thus fractures under minimal load. As a result their potential applications are very limited.
For instance, U.S. Pat. No. 4,206,095 discloses a process for producing particulate resoles from aqueous dispersion which combines 100 parts phenol and 90 parts formalin (i.e., a 0.9 formalin/phenol, F/P ratio). Hexamethylenetetramine is used as a catalyst with gum arabic as a protective colloid. As described therein the components are combined at about 85° C. for about 2.5 hours to form the phenolic spheres. The spheres formed in this manner are curable and will melt and coalesce, thus are unsuitable in any high temperature applications.
U.S. Pat. No. 4,366,303 discloses a process for producing particulate resoles with improved cure rate and sinter resistance which combines 100 parts phenol with 72 parts formalin (0.72 F/P ratio), hexamethylenetetramine as a catalyst with polyvinyl alcohol at about 0.4 parts per 100 parts phenol as a protective colloid. As described therein the components are combined at about 85° C. for about 1 hour and 10 minutes to form the phenolic spheres. Again, even though the spheres formed in this manner are curable but they will still melt and coalesce, thus are not suitable for high temperature applications.
Finally, U.S. Pat. No. 4,748,214 discloses a process for the production of microspherical cured phenolic resin particles having a particle diameter of not more than about 100 μm formed from novolak resin, which are useful as modifier or filler for various plastics and rubbers.
Accordingly, it is an object of this invention to provide high temperature resistant phenolic spheres exhibiting improved thermo-mechanical properties, among others. It is further an object of this invention to provide cured phenolic spheres of narrow size distribution which exhibit high compressive strength. It is further an object of this invention to provide cured phenolic spheres having hitherto unattainable compressive strength and do not fracture even when subjected to very high loads and retain the shape when the load is released. The phenolic spheres of this invention therefore find a number of applications where such high temperature and compressive strength materials are needed, including as reinforcing agents in a number of applications.